GSK598809 is being developed as an innovative treatment for substance dependence and potentially other compulsive behavioral disorders. This study will asses the effects of a single dose of GSK598809 in modulating nicotine reward in 2 cohorts of otherwise healthy male volunteers who smoke. Each cohort of subjects will receive a single dose of placebo or GSK598809 in two dosing sessions binded crossover fashine. There will be a washout period of at least seven days between each session.